1. Field of the Invention
The present invention relates to a technology to control pressurized state and pressure releasing state of a nip portion when a door is opened during an image forming operation and an interlock circuit is operated in an image forming apparatus.
2. Description of the Related Art
In Some business machines including an image forming apparatus, e.g., a printer and a multifunction peripheral, an interlock circuit to protect user's safety is installed. In particular, power supplied to a driving device such as motor is interrupted depending on a state of door switch (interlock switch). The door switch is arranged to link to an opening and closing of a front door or to an opening and closing of a right door of the machine. It means that if the front door etc., is opened, even when it is in a state that the power is supplied to the machine (powered on state), it is controlled such that driving voltage is not applied. This enables to prevent occurrence of incident such as electrocution of a user.
For example, as an interlock circuit installed on such a machine, Japanese Patent Application Laid-open No. 2012-230245 discloses an interlock circuit employing a relay for interrupting power supply line of the driving circuit to thereby interrupt the driving circuit of the relay by the interlock switch.
Also, conventionally, a fixing unit is provided on a general image forming apparatus. The fixing unit is a unit for fixing toner image on a recording material. The fixing unit is configured to melt and fix toner on the recording material by giving predetermined pressure and predetermined heat to a recording paper.
In an image forming apparatus which interrupts power supply of the driving circuit in conjunction with door opening, when the user opens door of the machine while the image forming apparatus is in the image forming operation, power supply of the driving circuit is interrupted by the interlock circuit. This results in an occurrence of a phenomenon in which the recording material is jammed in a conveyance path of the recording material (hereinafter, the phenomenon is referred to as JAM. Also, the recording material remaining in the conveyance path is referred to as a JAM paper).
Also, at this time, as to a driving circuit for performing pressure releasing operation to the nip portion between a pressure roller and a fixing roller in the fixing unit, its power supply is interrupted. Therefore, it becomes impossible to perform pressure release operation, which makes it difficult to remove JAM paper which is stopped at the nip portion.
Also, a fixing system which is quickly raised is known in the art. In the fixing system, a fixing film is used as the fixing roller to heat the recording paper. In such a system, when JAM occurs, the user may remove JAM paper (the process of removing the JAM paper is hereinafter referred to as JAM process).
At this time, when the recording material is removed with the recording paper is pressurized at the nip portion, the apparatus and the recording material may be damaged. Particularly, the fixing film in the fixing unit may be damaged or the JAM paper may be torn. This is a problem